Both slavery and serfdom inflicted enormous suffering on those subjected to their myriad indignities. The systems were based on exploitation and cynically used those at the bottom of the heap to enrich a wealthy, privileged few. That said, there were differences between American slavery and Russian serfdom. The most important was that Russian serfs were still considered citizens, albeit in a distinct category. Controversially, each American slave was regarded as three-fifths of a citizen under the notorious compromise that helped to ensure agreement on the United States Constitution.

Russian serfs, unlike American slaves, were liable to military service. Conditions in the Russian Army were notoriously harsh. Men were recruited at the age of 20 for a period of 25 years. The numerous hazards of military life, combined with a desperately low level of life expectancy, all but guaranteed that when a serf was conscripted he would never see his family or his village again. To make things worse, the Army often devised ways of making military service last for life—such as the imposition of extra service as punishment for often trivial disciplinary offenses—even if serf soldiers managed to survive their initial period of enlistment.

In the United States, the very idea of training slaves in the use of weaponry would have been anathema to their owners, who were always worried about the prospect of slave rebellions.

I tend to think that both conditions are similar in that bondage is the shared trait in both.  Serfdom in Russia involved the exploitation of one person at the hands of a wealthier and more powerful other.  This is the same in the American South, where the slave found themselves as manipulated by the White plantation owner.   In both, violence was used to ensure that obedience was displayed.  Yet, I tend to think that American slavery was more horrific in its implications.  For example, the Russian serf was never taken from an external country and traded on the block with as much frequency as the American slave.  The Middle Passage and slave auction could be two distinguishing factors in the American slave experience differing with the Russian serfdom. Another significant difference between both conditions is that the ending of the Russian serfdom happened more as a consequence of the passage of time.  American slavery only comes to an end because of the brutal and intense nature of the Civil War.  There is little else that brings about the end to the institution of American slavery, an upheaval and intensity not seen in the Russian serf condition.